A wide variety of lesions, including internal hemorrhoids, polyps, and mucositis, may be treated by ligation. Ligating bands and severing snares are two types of devices commonly used to sever targeted lesions from surrounding tissue.
When performing ligating band ligation, a ligating band is initially placed over the targeted lesion or blood vessel section. As a ligating band is typically elastic in nature, the band must be stretched beyond its undeformed diameter before it can be placed over any tissue. After the tissue to be ligated has been drawn within the inner diameter of the ligating band, the band is allowed to return to its undeformed size and therefore apply inward pressure on the section of tissue caught within the band. The effect of the inward pressure applied by the band is to stop all circulation through the targeted tissue, thereby causing the tissue to die. In due course, the body sloughs off the dead tissue and allows it to pass through the body naturally.
Ligating band dispensing means are used to facilitate the placement of a single ligating band or a set of ligating bands over the targeted tissue. Two examples of ligating band dispensers are U.S. Pat. No. 5,356,416 to Chu et al. and U.S. Pat. No. 5,398,844 to Zaslavsky et al., both of which are incorporated herein by reference.
Alternately, a lesion may be removed through the use of an electrosurgical severing snare. Electrosurgery can be defined as the use of a radio frequency electric current to sever tissue or achieve hemostasis. A high radio frequency is used because a low frequency (i.e., below 100,000 Hz.) will stimulate muscles and nerves and could injure the patient. Electrosurgery is typically performed at frequencies of approximately 500,000 Hz., although frequencies as high as 4,000,000 Hz. may be used.
Medical diathermy is similar to electrosurgery in that radio frequency current is passed through the patient's body. The major difference between these two techniques is the density of the radio frequency electric current; the current density used in medical diathermy is kept low so as to reduce tissue heating and prevent necrosis.
There are three surgical effects that can be achieved with electrosurgery. These include electrosurgical desiccation, which is a low power coagulation caused without sparking to the tissue; electrosurgical cutting, where electricity sparks to the targeted tissue and produces a cutting effect; and electrosurgical fulguration, where electricity sparks to the targeted tissue without causing significant cutting.
The above-described surgical effects can be accomplished by using either a monopolar or bipolar output. For many applications, however, bipolar output is preferable because the patient return electrode (necessary in monopolar procedures and a common source of accidents) is eliminated, and any desiccation performed is extremely localized because, in a true bipolar operation, only the tissue that is grasped between the two electrodes is desiccated. Bipolar output, however, is poor for cutting or fulgurating, and thus monopolar tools remain commonplace. Severing snares, for example, are almost all monopolar instruments.
Three types of electrical current waveforms are typically used in electrosurgery. These include a "cutting" waveform, which cuts tissue very cleanly but may cause the incised tissue to bleed excessively; a "coagulating" waveform, which desiccates and fulgurates tissue without significant cutting; and a "blended" waveform, which is a cutting waveform that has a moderate hemostatic effect. A waveform's "Crest Factor" describes the degree of hemostasis that waveform can produce if properly applied.
To remove a lesion (or polyp) with an electrosurgical severing snare, a wire snare is looped around the targeted lesion. Next, the lesion is desiccated and is cut through electrosurgically. It is also possible to sever the lesion in a single step. By cutting with a "blended" current, it is possible to cut through a lesion in one pass without having to worry about bleeding. Alternately, a lesion may be cut through mechanically with a thin snare wire after the blood supply to the targeted tissue has been coagulated and the tissue softened by a desiccation current.
After the targeted lesion has been severed from the surrounding tissue, the severed tissue may be aspirated into an endoscope or similar device. In this manner, a sample may be retrieved for further study. Alternately, the severed tissue can be allowed to pass through the body naturally.
While bands are more effective in removing tissue while controlling bleeding, snares allow severed tissue to be retrieved and allow a user to cut deeper into the tissue, when increased suction is applied, to ensure, for example, that all diseased tissue is removed at once.
Electrosurgical cutting, however, is a difficult technique to master, especially when cutting large or sessile polyps. When using the "two step" cutting method (i.e., desiccation before cutting) whether the actual cut is to be made mechanically or electrosurgically, a precise amount of desiccation is required. If there is too little desiccation, the stalk may bleed when cut. If there is too much, the stalk may become too hard and dry to cut either mechanically or electrically. It is also exceedingly difficult to master "one step" cutting, which uses a blended current to ensure sufficient hemostasis. This is especially true when thick snare wires are used or a current with a high Crest Factor is applied. Often it will be very difficult to start cutting a given polyp. Thus, at times it may be desirable to use a pure cutting waveform to get the cut started. However, this may result in serious bleeding because the polyp has not previously been properly desiccated.
Currently, if it is desired to alternate between ligating band ligation and the use of electrosurgical snare, one or the other of these two types of instruments must be inserted through the working channel of an endoscope. Finishing with the first device, the user would have to withdraw this device from the endoscope before replacing it with the second device. In treatment of multiple lesions, for example, this process may need to be repeated several times, wasting the user's time, exposing the instruments to possible contamination during removal, and increasing the time and discomfort associated with the procedure.